1. Field of the Invention
The present invention relates to an improved device for obtaining a sample of fiber from a fiber processing plant, such as a pulp or paper mill, a corn plant, or a starch plant. The improved fiber sampling device has several advantages over current sampling devices, including the ability to fully flush, in order to remove residual fiber, and the ability to be installed and removed while the plant is running. The improved fiber sampling device, therefore, allows fiber processing plants to obtain useful samples more easily and with less contamination than with current sampling units.
2. Brief Description of the Prior Art
A large number of industries are based on the processing of natural fiber. The pulp and paper industry, for example, converts wood fiber to pulp and paper products. The corn processing industry converts corn to starch, sugar, corn oil, and other products. Other crops, such as wheat and soybeans, are processed in an analogous manner. Cotton fiber is processed to make clothing and other textile goods.
One need that this wide range of industries has in common is the need for fiber sampling. All of the fiber processes are run at specified conditions (temperature, pH, salt concentration, etc.) and are run to a given degree of processing (chemical reaction, purity, removal of inhibitors, etc.). Although a good deal of automated instrumentation is available to monitor and control these process variables, in almost all plants there are some process variables that are not controlled automatically, and samples of the fiber are required for process control. In addition, most automated controls require occasional (or frequent) calibration with actual samples.
Much sampling of fiber is carried out manually. Manual fiber sampling consists of grabbing a sample of fiber with one's hands or with a scoop, where the fiber is openly exposed. If the fiber is flowing within a stock line, a manual sample can be taken by opening a valve attached to the line and using the pressure in the line to force the sample out. The sample is collected until the desired quantity is obtained, and the valve is then closed.
A more sophisticated form of manual sampling consists of two valves in series, connected by an intermediate pipe that is 6 to 12 inches long. The valve closer to the stock line, hereinafter referred to as the first isolation valve, is opened and closed to take a sample; the valve farther from the stock line, hereinafter referred to as the second isolation valve, is closed except when removing a sample from the pipe. To take a sample, the first valve is opened to fill the intermediate pipe with fiber. The first valve is then closed, and the second valve is opened to allow removal of the fiber sample.
An advantageous variant of the two-valves in series is to add a third valve to the system, which is attached to a T coming off the intermediate pipe. This third valve can be opened to allow water into the intermediate pipe, and force the fiber sample out when the second isolation valve is open.
Such a known three-valve sampler can be installed on-line, that is, while the plant is running, and fiber is flowing through the stock line under pressure. This is advantageous, as it avoids the need to shut down the mill to install the sampler. On-line installation is carried out using a so-called hot-tap procedure. A first valve is connected to one end of a pipe nipple, the other end of the nipple then is welded to a stock line. A hot tap apparatus is attached to the other part of the first valve. The valve is opened; a drill bit is pushed through the opening within the valve body; until it bores through the wall of the stock line. The drill bit then is removed through the valve body and the first valve is closed. A first valve so attached to the stock line then is ready to be attached to an intermediate pipe and a second valve.
There are several disadvantages associated with known three valve systems. First, there is no water flush between the first valve and the stock line, and fiber can build up at this point, and contaminate subsequent samples. Second, there is no technique to remove the entire system on-line, for cleaning or maintenance.
While operation of known three valve samples can be automated, so as to allow the samples to be taken automatically, such automation does not overcome the inherent disadvantages of the unit during automatic sampling.
For frequent or multiple samples, and for situations where a sample must be moved a large distance for analysis, certain automated sampling units are known. Several known commercial sampling devices are listed in Table 1. These devices are used for specific solids consistencies, pipe diameters, process temperatures, and materials of construction. In each device a sample is conveyed to a desired location or instrument by either:
1. Internal pressure in the stock line, which feeds the sample directly to the instrument a short distance away.
2. A piston-type pressure, where a moving piston conveys a sample of fiber a distance of 50-200 feet.
3. A flowing-type, where water conveys the sample to the instrument.
A typical example of such devices, is the Kajaani SD-503, which contains a sampling valve element that is inserted into the stock line, and is electrically actuated from outside the stock line. The tip of the sampling valve is a plunger that opens and closes to admit a sample. This sampling valve is short (with a length less than two inches), and has an inlet port coupled to the stock line by a process coupling. The outlet part of the sampling valve is attached to a sample chamber. The pulp samples pass through a sample chamber and out of a hose, to a remote location. Water is admitted to the sampling chamber, at a point just downstream from the process coupling. This water is used to convey the samples out of the sample chamber, and into the hose.
One shortcoming of the SD-503 sampling device is the inability to do a complete water flushing of the sample chamber. The system is not designed for flush water to penetrate all the way to the sampling valve element. In addition, crevices within the sample chamber catch and hold fiber. This makes fiber buildup at or near the isolation valve likely, which causes cross contamination of samples. Another shortcoming of the SD-503 sampling device is that it cannot be installed or removed on-line. The requirement to shut down the plant or fiber line before installing or removing the sampling valve element is a serious inconvenience, and cost factor.
TABLE 1 ______________________________________ AUTOMATIC SAMPLING DEVICES MANU- SOLIDS PIPE SPECIAL FACTURER UNIT CONSISTENCY DIAMETER FEATURES ______________________________________ ABB 1000 &lt;6% not specified EPDM seal 1001 &lt;6% not specified Viton seal 1002 &lt;6% not specified Screens sample 1003 6-14% not specified EPDM seal 1004 6-14% not specified Screens pulp MCB- 6-14% not specified Screens pulp 1003 BTG HDS- &gt;12% not specified temp &gt;150 C. 1010 HDS- &gt;12% not specified temp &gt;150 C. 1100 MDS- 5-12% not specified 1100 LDS- &lt;5% not specified 1100 KAJAANI SD-501 6-15% not specified piston type SD-502 0.5-6% &lt;8 inches flow type SD-503 0.5-6% &lt;4 inches titanium ______________________________________
Therefore, in spite of the availability of a wide variety of fiber samplers, there are significant shortcomings with such known devices. Those shortcomings are addressed by the present invention.